38 THEORY OF EVOLUTION 



bring about variations. If his views seem to us 

 today at times vague, at times problematical, 

 and often without a secure basis, nevertheless 

 we find in every instance, that Darwin was 

 searching for the physical causes of variation. 

 He brought, in consequence, conviction to 

 many minds that there are abundant indica- 

 tions, even if certain proof is lacking, that the 

 causes of variation are to be found in natural 

 processes. 



Today the belief that evolution takes place 

 by means of natural processes is generally ac- 

 cepted. It does not seem probable that we 

 shall ever again have to renew the old contest 

 between evolution and special creation. 



But this is not enough. We can never re- 

 main satisfied with a negative conclusion of this 

 kind. We must find out what natural causes 

 bring about variations in animals and plants; 

 and we must also find out what kinds of varia- 

 tions are inherited, and how they are inherited. 

 If the circumstantial evidence for organic evo- 

 lution, furnished by comparative anatomy, 

 embryology and paleontology is cogent, we 

 should be able to observe evolution going on at 



